Radio frequency (RF) power amplifiers are utilized in RF communication systems to increase the power of an input RF signal to allow the signal to be transmitted over a transmission channel (e.g. through an antenna). The gain response and efficiency of a given power amplifier depends on its design. Many power amplifiers fall within certain classes (i.e. classes A, B, C, E, F and J) that specify the general characteristics of the amplifiers.
Many communications, broadcast and wireless standards like Long-Term Evolution (LTE), Digital Video Broadcasting (DVB), Integrated Services Digital Broadcasting (ISDB) and 802.11ax are based on orthogonal frequency division multiplexing (OFDM) modulation. In addition, the Advanced Televisions Systems Committee (ATSC) are planning to introduce OFDM in future standards. Although OFDM is very spectrally efficient, it does so at the expense of a high peak-to-average power ratio (PAPR).
Single device radio frequency power amplifiers are capable of achieving high efficiency only at their peak output power (POUT), which is significantly degraded as POUT is reduced. To avoid reaching the peak output power and thereby hitting saturation point, communications, broadcast and wireless connectivity signals generally require that on average the power amplifier operates significantly below the peak output power, while still being able to accommodate the large signal peaks. Operating an amplifier at an average power below the maximum power is referred to as “backing-off”.
Backing-off in light of a high PAPR therefore leads to a low average efficiency for a single device radio frequency power amplifier. There is therefore a need for a radio frequency power amplifier with improved efficiency for systems with a high PAPR.